Cob: Using quicklime in mixes

[Mike Wye]

Using quicklime as opposed to lime putty:
1. There was a tradition in some areas of Devon of adding quicklime directly
into cob mixes, the quicklime reacts with the water in the cob mix, thus
reducing drying time both by the removal of water and the introduction of
heat from the slaking process. The calcium hydroxide formed has the usual
effect of soil stabilisation in high clay content soils
2. Masons mortar for construction purposes was also made in some cases by
covering a pile of quicklime with washed, damp sand and then turning the
pile over after a few days. This "hot lime" mix was used for building stone
walls where any resultant popping of unslaked quicklime would not be
critical and was a cheaper method than slaking first, so where cost was the
sole criteria ... For plastering and rendering it would always have been
lime putty as any popping would be obviously detrimental to the finished
work.
regards,
Mike
Mike Wye & Associates,
Traditional & Ecological Building Products
www.mikewye.co.uk
01409-281644
sales at mikewye.co.uk
----- Original Message -----
From: "Charmaine R Taylor" <tms at northcoast.com>
To: "Matthew HALL(SED)" <M.Hall at shu.ac.uk>; <coblist at deatech.com>
Sent: Friday, January 11, 2002 6:58 PM
Subject: Re: FW: Cob: clarification on Quick lime vs hydrate


> Hi Matt, you misread what I wrote  I did NOT say it's quick lime AFTER
> it's slaked in water (hydrated.)..I know better.
>
> I have not read anything anywhere about  freshly made quicklime being
> added  DIRECTLY to clay. If this is a new process, it's new to me.  None
> of the National Lime inst. info details use this way to my knowledge.
>
> Now, freshly slaked quicklime is left in sufficient water to be a lime
> putty/paster, and that is added to high clay soils to stabilize them.
> Stickly Gumboil or Montmorillonite clays are so water loving they need
> the lime to balance them.
>
> In your method/ description where does the quicklime GET its water?
>
> As for the LIME :WATER warning asked by Ocean..ALWYS add lime to water,
> even dry hydrate that HAS been processed. You never know if an unslaked
> bit will "pop" exploding lime powder into you face.  This can burn you.
> Here is the slaking process:
> Fresh roasted Quicklime "thirts" for water..that's why it's called
> "slaking" when the hot lime is put into water...the lime "takes" the
> water it needs, and drives off the rest in an exothermic reaction
> (heat:steam) until a dry powder is achieved.  Sometimes it is left in
> enough water to be a lime putty.  Too much water or too cold of water
> "drownd" quicklime so it is unreactive, to little water to to high a
> heat generated is called "dead burned", and is also unreactive. This is
> why the ASTM guidlines are strict to produce a perfectly useable, fine
> powder lime.
>
> Messing with quicklime for the averageperson  can be dangerous, and the
> results uneven at best. Even Ianto and others who ARE savvy make
> mistakes... quicklime can boil off and melt stuff, explode, start fires,
> and injure people.
>
> Charmaine  Taylor/ Taylor Publishing
> http://www.dirtcheapbuilder.com
> http://www.papercrete.com
> PO Box 375, Cutten CA 95534
> 707-441-1632
>
>